The invention relates to a supporting pipe for constituting a drive unit for an automotive vehicle, comprising an engine with clutch and transmission unit, whereby the engine is disposed at the front and the transmission in the rear, connected as a unit with interposition of the supporting pipe.
A supporting pipe is known (German Offenlegungsschrift No. 23 60 514 and U.S. Pat. No. 3,998,290) that consists of a single pipe and presents uniform wall thickness. This supporting pipe is almost rigidly connected as an assembly with a rear transmission unit and a forward engine. Use of such a supporting pipe has disadvantageous effects on the whole system because vibrations are produced by the spectrum of excitation of the engine and the transmission that cause vibrations on the whole assembly and thereby cause noise. Flexion and torsion resonances develop especially strongly in this type of construction, so that, as a whole, comfort that could be provided by acoustic and vibration technology is reduced.
The invention concerns the problem of creating a supporting pipe for an engine-transmission assembly of the type in question in which there will be a reduction of vibration and also of noise.
This problem is solved according to a preferred embodiment of the invention in that the supporting pipe is constituted by at least one outer pipe and an inner pipe fitted therein, which are interconnected at one end and are held in position via a friction seat.
It is further provided that there is a layer of elastic vibration-damping material between the respective pipes. According to another embodiment of the invention, the outer pipe is made shorter than the inner pipe and held with one end in the flange that is to be connected to the transmission housing. It is further provided that the inner pipe supports a plurality of outer pipes that are of different lengths and whose common terminal ends are held in the transmission flange. It is further provided according to the invention that the outer pipe is connected with the flange, and on the other hand the pipes have a fixed interconnection only in the region of the transmission flange. The pipes according to various forms of embodiment of the invention can present an equal or a different wall thickness. Also, the supporting pipe can be made in a mixed construction whereby the outer pipe or pipes are of steel and the inner pipe is of a light metal alloy.
The advantages created by the invention include that vibrations are reduced and thereby noise is diminished. Vibration tests on the supporting pipe with incorporated drive have shown that because of the pipes set one inside the other a relatively pronounced reduction of vibrations is produced in the range of bending and torsion oscillation. Pipes with an intermediate layer advantageously produce a supporting pipe that is impermeable to air noise, whereby bearing and transmission noises can be reduced.
This behavior is especially at its most favorable when the pipes present the same wall thickness. This effect is possible because a partial conversion of oscillation energy into heat can occur because of the mechanical friction between the pipes, and the energy conversion has a damping effect on the oscillations. The supplementary fixed interconnection of the pipes in the region of the transmission flange effects a stiffening of the supporting pipe in the flexing direction, because the two pipes are in positive engagement in the region of the transmission, where a relatively high driving moment has to be backed up. By this connection it is further managed that in torsional excitation the pipes maximally rub against each other, so that reduction of vibration is achieved.
For weight reduction, the outer pipes of the supporting pipe can be made shorter or longer, corresponding to the increasing load in the direction of the transmission. Also, there can be a mixed construction of the pipes which may be for example made of aluminum, steel, fiberglass reinforced plastic and CFK.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.